Speaker
Description
For the successful employment of Li-ion batteries at large scale, e.g. for electrical vehicles or stationary energy storage, a crucial point is to increase of energy density in the battery. In order to increase this parameter, anode conversion-alloy materials, such as SnO$_2$ with a specific capacity of ~ 1500 mAh/g, are a serious choice, in particular when mixed with graphite. Despite the theoretical predictions of the different SnO$_2$ conversion and alloy reactions during (de-)lithiation, the experimental identification of those electrochemical reactions and the formation of intermediate species (e.g. $Li_aSnO_b$, $Li_xSn$ and $Li_2O$) is not fully understood,$^1$ mainly due to their possible relaxation and conversion to other byproducts during disassembling of the cycled cell in post mortem analysis.$^2$
In this contribution we explore the capabilities of our recently developed operando X-ray photoelectron spectroscopy (o-XPS) to monitor in real time the evolution of the electrolyte-electrode interface and the (de-)lithiation processes of the active materials during solid state Li-ion battery operation.$^3$ In particular, we present the results of our study on the (de-)lithiation of the SnO$_2$ particles in a working electrode composed of SnO$_2$ nanoparticles, (Li$_2$S)$_3$-P$_2$S$_5$ (LPS)$^4$ solid electrolyte (SE) and Super P as conductive carbon cycled versus InLi$_x$ counter electrode (Figure 1a). The analysis of the Sn 3d (Figure 1b), Sn 4d, O 1s (Figure 1c) and Li 1s spectra reveals the progressive conversion of the SnO$_2$ particles to form $Sn^0$ and the simultaneous formation of the $Li_xSn$ alloy. When the potential is below 0.4 V (vs. Li$^+$/Li), the $Li_2O$ phase is formed and grows until the full lithiation at 0.01 V (vs. Li$^+$/Li), where the only species observed are $Li_2O$ and $Li_xSn$. During the de-lithiation process, the partial reversibility of the conversion-alloy reactions takes place, where $Li_xSn$ is converted to $SnO_x$ at 2.5 V (vs. Li+/Li). The S 2p and P 2p core levels reveal the presence of reduced $Li_2S$ byproduct species below 1.6 V (vs. Li+/Li), in accordance with previous studies.$^4$
References:
[1] Y. Cheng, A. Nie, L.-Y. Gan, Q. Zhang, U. Schwingenschlögi, J. Mater. Chem. A, 2015, 3, 19483
[2] G. Ferraresi, C. Villevieille, I. Czekaj, M. Horisberger, P. Novák, M. El Kazzi, ACS Appl. Mater. Interfaces, 2018, 10, 8712-8720
[3] X. Wu, C. Villevieille, P. Novák, M. El Kazzi, Phys. Chem. Chem. Phys., 2018, 20, 11123
[4] X. Wu, M. El Kazzi, C. Villevieille, J. Electroceram., 2017, 38, 207-214
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